Preliminary studies suggest that pregnancy is associated with altered immune responses. 1) Peripheral blood lymphocytes from pregnant women exhibited a decreased response in vitro to pokeweed mitogen (a B and T lymphocyte mitogen), whereas their response to phytohemagglutinin (a T lymphocyte mitogen) is normal. 2) Sera from pregnant women inhibit lymphocyte responses in vitro. Investigation of the influence of pregnancy on immune responses will include the following approaches. 1) To assess the immunocompetence of peripheral B and T lymphocytes with various mitogens. 2) To determine shifts in the proportions of perpheral blood B and T lymphocytes during pregnancy. 3) To study the mechanisms underlying the B lymphocyte unresponsiveness by enzymatic removal of lymphocyte surface proteins which may hinder the mitogen-B lymphocyte interaction. 4) To evaluate the incidence of serum lymphocyte inhibitors during pregnancy. 5) to isolate and characterize serum lymphocyte inhibitors employing sephadex and iso-electric focusing. 6) To define the alterations of humoral and cell-mediated immune responses in pregnant laboratory mice using sheep erythrocyte immunization, agar hemolytic plaque method, migration inhibitory factor assay, and lymphocyte blast transformation technique.